Several things cause the rising of cake batter, which results in a cake with a fine, tender, light crumb.

The reaction of baking soda or baking powder with the liquid in the batter: These ingredients react together and cause air bubbles to form. It's important to use baking powder that is not outdated (check the date on the container).

Beating air into the butter or shortening and sugar: This step is very important and cannot be cut short. Follow the timings for beating in the recipe closely.

Introduction of eggs into the batter: Eggs, when beaten, add air to the batter, so it depends on what type of cake you are making as to how much the eggs are beaten. Sometimes the yolks and whites are beaten separately. Again, make sure to follow the timings in the recipe when beating in the eggs.

Heat of the oven: The heat of the oven can cause baking powder to react further and cause more air bubbles, and the heat also sets the structure of the cake. The proper oven temperature is important to allow the cake to rise first before the structure sets. If the oven is too hot, the cake will set too fast before the air bubbles have a chance to form. Or, if the oven is not hot enough, the cake will rise too much, then fall in the center before it is set. To check your oven temperature, bake a cake mix cake. If the cake is done properly within the time range on the package, your oven is most likely baking at the proper temperature. If not, consult your manufacturer's directions or consult an appliance expert on how to adjust the temperature up or down.